1. Field of the Invention
The present invention relates to a semiconductor accelerometer and, in particular, relates to a semiconductor accelerometer suitable such as for actuating an air bag in a motor vehicle and for controlling a motor vehicle.
2. Description of Related Art
FIG. 17 illustrates one example of a capacitance type semiconductor accelerometer as disclosed in U.S. Pat. No. 5,095,752 wherein a weight 5 for sensing an acceleration is formed in a silicon plate 1 by etching while being supported by a cantilever portion 10 connected to the outer frame portion of the silicon plate 1. The silicon plate 1 is sandwitched between glass plates 4 and 9 via a bonding material. Stationary electrodes 13 are formed on the respective surfaces facing the two major surfaces of the weight 5 which serves as a movable electrode in response to acceleration acting thereon and a capacitance change caused thereby is transmitted to a signal processing unit (not shown) through bonding pads 8.
In the above capacitance type semiconductor accelerometer, the center of gravity indicated by an asterisk on the weight 5 is designed to be located on a parallel plane containing a center line in the thickness direction of the cantilever portion 10.
JP-3-214064(1991) also discloses a semiconductor accelerometer using piezo resistances for detecting an acceleration having a similar weight configuration as the above.
In the above conventional art, the mass portion constituting the weight for sensing an acceleration was formed by processing the silicon plate itself, and a microscopic processing which uses a double side alignment of several times was. Therefore it was difficult to manufacture such semiconductor accelerometers with a sufficient processing accuracy. For this reason, a mass-production of such semiconductor accelerometers was difficult.